Selectively vented connectors for percussion bits



Sept. 30, 1969 w, BECKER 3,469,640

SELECTIVELY VENTED CONNECTORS FOR PERCUSSION [HTS Filed Feb. 12, 1968 s Sheets-Shet 1 FIGZ.

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NV TOR. 520 W 2 am M BY firgA/T 495M7- United States Patent 3,469,640 SELECTIVELY VENTED CONNECTORS FOR PERCUSSION BITS Floyd Walter Becker, Calgary, Alberta, Canada, assignor to Becker Drilling (Alberta) Ltd., Calgary, Alberta, Canada Filed Feb. 12, 1968, Ser. No. 704,814 Int. Cl. E21b 17/04 U.S. Cl. 175--321 7 Claims ABSTRACT OF THE DISCLOSURE An apparatus for drilling a borehole which consists of an annular toothed bit and a double walled drill pipe having an annular space and a central passage. A sleeve connector having double walls defining a chamber is connected between the bit and the lower end of the drill pipe. Fluid is supplied through the annular space and the chamber and discharged from the bit teeth to entrain fragments and transport them up the central passage. The bit has elongated holding elements 'guidedly movable in the sleeve connector so that when the bit is in an extended position ports are opened between the elements in communication with the sleeve connector chamber and the central passage and with the annulus of the borehole so that fluid currents scour the borehole annulus. Fragments accumulated in the borehole annulus are thereby cleared and transported up the central passage.

This invention relates to earth drilling apparatus and in particular concerns venting means for use with percussive drilling bits to clear accumulated fragments from the annulus between a borehole and a drill string, for the purpose of preventing such fragments from jamming the bit as the string is raised.

In relatively rigid ground which has little or no plasticity, as certain shales and sedimentary deposits which are otherwise weak and sufiiciently brittle to render them penetrable by percussion drilling, a problem encountered is the tendency of the drive pipe to bind in the borehole while being raised. The problem arises from the shaking down of loose earth mateirals that crumble away from the sides of the borehole and accumulate in the annulus surrounding the drill pipe to varying depths above the bit. The problem is aggravated in ground in which the borehole departs from straightness and becomes twisted or skewed, so that rubbing and lateral vibration of the drill string under the shock of hammer blows loosens a larger quantity of fragments. In a drilling operation using the method and apparatus as is described in US. Patent 3,280,925 the bit usually has the form of a thick annulus with tapered exterior surface, and the maximum bit diameter is usually a fraction of an inch greater than the pipe diameter to facilitate movement of pipe along the borehole. Because the bit body is inherently the same diameter as the borehole, it acts as a plug, so that in the raising of the drill string any materials in the annulus surrounding and above the bit must be crowded into the sidewalls to allow the bit to pass upward. Provided that the sidewall materials are reasonably yielding, that is, if they comprise materials having plasticity adequate for the compaction of fragments into the undisturbed ground, the drill bit may be successfully raised by application of sufficient lifting pulls. When however, the materials have insufiicient plasticity, it will be found that after a small initial movement of the hoisting jacks the load rapidly increases, and further upward movement is stopped, with the drill pipe and bit effectively jammed in the borehole. The jamming results from the lateral and upward compaction of the earth material in the an- "ice nulus. The driller may attempt to drive the pipe down again, followed by a succession of lifting .pulls after each drive in an effort to release the jam. He may also resort to washing the exterior of the drill pipe with water or bentonitic clay slurries led into the annulus at the surface, with the objective of lubricating the materials in the area of contact with the tapered surface of the bit. These expedients however fail in situations where the borehole wall is strong and unyielding and the fragments are mainly strong gravel. Extreme lifting pulls may tear the string apart in tension leaving valuable equipment in the hole and necessitating recovery procedures or even starting .a new borehole. The problem occurs also where there is a radial step or shoulder at the junction of the bit with its connector. It appears to be ineffectual to reduce the taper of the exterior of the bit body as jamming occurs when the annulus is a small fraction of an inch.

The present invention overcomes the problem by providing a selectively vented bit connector in which, during the raising of the pipe, ports having large area are opened in the sides of the outer pipe to communicate with the high pressure fluid supply in the adjacent annular passage between the drill pipes and to communicate also with the central passage of the inner pipe. As the ports open the fluid flows vigorously outward against the fragment mass in the annulus, scouring the borehole wall and entraining the materials in turbulent flow. This flow carries the fragments into the central passage along which they are conveyed to the surface and discharged as normal cuttings, a small portion only falling to the bottom of the borehole. As a consequence the bit is free to pass upward along the borehole without encountering substantial fragment accumulations and the air supply may be disconnected. Incipient further jamming may be relieved readily by simply lowering the drill bit a short distance to avoid compaction of accumulated fragments and the string is then lifted a few inches to open the ports again, while the air pressure is reapplied.

In carrying the invention into effect with a doublewalled drill pipe and an annular toothed bit such as are described in the aforesaid US. Patent 3,280,925 for percussive drilling of overburden using high-energy hammer means impacting the upper end of the drive pipe and employing compressed air circulation for jetting air from tooth nozzles for elevating fragments up the central passage, a double-walled sleeve-like connector is provided between the lower end of the drill pipe and the bit, in which the bit is captively pinned. Hook-shaped upward extensions of the bit body reciprocably received in an annular space between the sleeve walls permit it to drop into a depending position whenever the drill pipe is raised with respect to the bit, thereby opening large area ports formed between the exposed hooks which communicate with the high-pressure air supply led between the sleeve walls and open also into the borehole annulus. Whenever the bit rests on the borehole bottom and the drill pipe is lowered to impress an axial load thereon, the upper face of the bit is firmly pressed against the lower margins of the sleeve and the ports are closed so that a negligible leakage of high pressure air flows to the annulus. The hooked extensions are entirely hidden within the sleeve.

The invention will be more readily understood both as to its concepts and practical constructions from a reading of the following description of its preferred embodiments, in conjunction with the accompanying figures of the drawing, in which:

FIGURE 1 is a rear elevation view of a percussive drilling apparatus of the prior art illustrating the problem of raising a drill pipe and bit in a borehole;

FIGURE 2 shows the lower end of the pipe and bit of FIGURE 1 in enlarged scale, detailing the jamming effect developed by compaction of earth and fragments in the borehole annulus;

FIGURE 3 is a graph wherein lifting pull is plotted against lift-distance for the bit of FIGURE 1, as jamming develops;

FIGURE 4 is a side elevation view partly in section through a borehole showing a bit and a vented bit connector according to the invention, the connector being in opened or annulus-clearing position, and,

FIGURE 5 is a perspective partly cut-away view of the elements of the bit and the connector of FIGURE 4 in pre-assembly relation.

Referring to the drawing, a double-walled drill string generally designated is shown in FIGURE 1 extending into the borehole 11 substantially as described in the aforesaid United States patent, the string carrying at its lower end a toothed percussive drill bit 12 of slightly larger diameter than the diameter of the drill pipe. The upper end of the drill pipe is closed by an anvil cap 13 to which a high pressure circulating fluid such as compressed air is supplied by hose 14 and from which elevated fragments (not shown) are carried away along conduit 15. The Weight of a percussive hammer means 16 (shown only in part) is supported on the drill string to impress an axial load on the bit 12. As the drill pipe descends in the borehole under the driving action of the hammer, fragments inevitably accumulate in the annulus 17, the greater part lodging just above the bit 12.

Elevating means for raising the drill string comprise the cradle 18 fitted with releasable pipe-grabs 19, and its support straps 20 carried by piston rods of the doubleacting hydraulic jacks 21. The latter rest on the base 22, which stands on the ground about the upper end of the drill pipe, which passes through the opening 23 centered in the base. The removal of a drill string as described in the said patent is accomplished by causing the hydraulic jacks to lift the cradle and thereby to grip the outer drill pipe, thus raising the string a distance determined by the lift of the jacks 21. When the jacks are subsequently retracted, grabs 19 automatically release and the cradle descends, enabling a succession of jack actuations to lift the string by increments. Additional grabs (not shown) may be inserted in opening 23 to prevent the pipe from sliding down the hole if earth friction should fail to hold it.

Where the ground is unyielding or insufiiciently plastic to afford a passage for the bit 12 through the annulus, a situation as depicted in FIGURE 2 is likely to develop after an initial short upward displacement of the bit, wherein the contents of the annulus 17 are firmly compacted and the bit and drill pipe have jammed immovably along the borehole. The elfect often occurs suddenly as may be seen from the graph, FIGURE 3, wherein the lifting pull increases abruptly at a certain upward travel of the bit; the graph shows that the resistance of the bit and pipe to be moved upward may far exceed the normal load experienced when the string and bit are free in the hole. As a consequence the lifting jacks may exert an upward pull beyond the safe limit of pipe joints. A length of pipe may also rupture in tension due to existence of bending stress induced by curvature of the borehole.

A novel bit connector generally designated 24 in FIG- URES 4 and 5 which provides for scouring of the annulus 17 and removal of any materials accumulated therein before these can be compacted by reason of upward movement of the bit 12, comprises an upper box end portion 25 for receiving the end 26 of the lower length of drill pipe, and a lower double-walled sleeve portion 27 in which the bit-carrying hooks 28 are held captive but telescopically movable. The inner and outer pipes 29 and 30 of the string 10 are spaced to provide between them the annular passage 31 to which high pressure air is fed from supply hose 14. A seal ring 32 closes the lower end of the annular passage, the ring seating in a groove 32 in the lower end of the pin end 26. The gaseous circulating fluid, which may be high pressure air, is fed through a number of radial apertures 33 opening through the pipe threading on the pin end and is distributed to the upper ends 34 of the bores which extend downwardly along the box end 25 which is threadedly engaged with the pin end. Impact energy is transmitted along outer pipe 30 to the thickened box end 25, whose bevelled and stepped lower end portion 37 is fixed as by welding to the upper ends of the inner and outer coaxial sleeves 38', 39, which comprises the novel bit connector of the present invention. The bores 35 communicate at their lower ends with the annular chamber 40 formed between the concentric sleeves and supply high pressure gaseous fluid thereto.

The bit 12 has chisel teeth 41 each having an inwardlyopening orifice 42 and an axial passage 43 opening upwardly in the raised and interrupted upper face ring 44. The upper face of the bit body 12 further comprises the annular seats 45 and 46 which lie respectively adjacently inside and outside the ring 44 and offset axially below the level of the ring 44. The lower margins 47 and 48 of the sleeves 38 and 39 rest upon the seats when the weight of the drill pipe is carried by the bit, effecting a gas seal for the lower end of the chamber 40. While this seal is not totally elfective, any leakage under the margin 48 is minimized and merely develops a slight flow toward the annulus 17. Where ground water is encountered, the small ascending gas flow tends to reduce the column head.

The upward projections 28 rising above the ring 44 comprise longitudinal cylindrical segments whose sectoral span is about 60 degrees are for a bit having three such segments. It is to be understood however that any convenient number, for example two, three, four or more shanks may be provided as appropriate to the Size of the bit and the pulling load therefor, and the sectoral span may be varied considerably provided that the gaps between the segments, hereinafter termed ports 50, are of adequate cross-sectional area to develop a suflicient flow when the connector is in extended or opened relation. The ports 50 are bounded along their vertical sides by the edges 28A and edges 51, and along their upper and lower margins by the margin 48 and the margin of ring 44. As will be best seen from FIGURE 5, the ports 50 open toward the borehole annulus 17 and inwardly toward the central passage 60.

The upper portion of each hook 28 is widened to span an are greater than the sectoral span of a shank portion thereof, as measured at the axis of the bit between the vertical edges 51 and 52 disposed on opposite sides of the hooked upper end. The widened portion has an under margin of upwardly concavely recessed shape, the re cesses 53 being semi-cylindrical and [being disposed tangent with the shank edges 28A.

Pins 54 extend radially through apertures 55 in the lower ends of the sleeve walls 38 and 39, there being as many pins as there are hook 28, to provide in the assembled relation that the recesses engage respective pins, as shown in the extended limit portion of the bit, FIG- URE 4. Relative rotation of the bit shanks 28 within the chamber 40 is prevented by the additional pin 56 passing through the lower ends of the sleeves 38, 39 and occupying radially-aligned apertures 57 therein. The angular location of pin 56 is such that one shank edge 51 slides along the pin while the' other vertical edge 28A slides along pin 54. Pin 56 is a press fit, enabling its removal so that the bit body may be removed from the connector 27 at any time by pressing the bit 12 upward to clear the hooks from pins 54, and rotating the bit thereafter to allow pins 54 to move along the edges 52.

In certain bit forms where the number of teeth 41 and their spacing results in obscuring some of the tooth passages 43 by reason of the positions of the hook shanks 28 overlying the teeth, angled passages 58 are drilled into the side edges 28A or 51 as required, to communicate with an adjacent tooth passage. Accordingly, high pressure fluid or air in chamber 40 finds its way to each tooth.

In the driving position, when the margin 48 rests on the annular seat 46 of the face of the bit, the leakage of the fluid or air is significantly minimized by shaping the margin 48 as a cone of vertical angle smaller than 180 but greater than about 120, and shaping the seat 46 to mate therewith.

It will be apparent from the foregoing description that the invention provides a positive and effective means for scouring fragments accumulated in the borehole annulus 17, which may at any time be put into operation merely by lifting the drill pipe a few inches as necessary to extend the shanks 28 and open the ports 50 while maintaining fluid pressure in chamber 40. The fluid or air discharge from the chamber 40 as vertical jets flowing between the opposed edges 51 and 52 of adjacent shanks, impinging the face ring 44 and developing turbulent vortexial flow in all open spaces. Fragments accessible to the vigorously moving fluid or air will become entrained and carried up the central passage 60. Those openings 43 impinged by the jets will convey fluid to the tooth orifices 42, developing an ascending flow along the lower end of the passage 60, tending to entrain and elevate any fragments which otherwise would fall to the borehole bottom. Since the spaces exterior to the tooth shanks 28 will also have a strong flow therein, fragments are effectively scoured out of a band or zone extending upwardly as far as the margin 48 of sleeve 27. As the drill pipe is pulled further up the borehole, the fluid or air successively impinges the exposed annulus 17 and removes fragments which would otherwise impede the bit. The flow may be continued as long as desired or necessary. If the flow is shut off and incipient jamming is detected as the bit moves along a higher part of the borehole, the operator has only to lower the pipe and bit a few inches to release fragments becoming compacted in the annulus, and then restore the fluid supply while again raising the bit. The opening of the ports 50 is assured both by the friction of the bit 12 against the sides of the borehole, and by the piston effect tending to force the bit down when fluid pressure is supplied to chamber 40.

The ports 50 also serve to dewater an annulus which has become flooded by ground water encountered in a stratum penetrated by the borehole, since the application of gas or air pressure when the ports are opened in connector 27 flushes liquid spillings into the central passage 60, and where the head is not excessive, water is lifted along the annulus to the surface. The annulus may be pressurized to resist outpouring of water thereinto, by periodically opening the ports 50 and maintaining pressure in chamber 40. As the ports are closed, the annulus is sealed at its lower end, while suitable packing means may be provided at the surface (not shown) to retain the pressure.

It will be apparent to those skilled in the art that numerous additional uses will be found for vented bit connectors according to the present invention, and it is intended that the foregoing description shall be interpreted as illustrative and exemplary of the construction and practices rather than as limiting of the invention, which is defined more particularly in and by the appended claims.

I claim:

1. In apparatus for percussion drilling of a borehole wherein an annular toothed bit is driven through earth materials by a double-walled drill pipe subjected to repeated impact and axial loading, said pipe defining an annular space and a central passage, wherein fluid is supplied to said annular space and is discharged from the bit teeth to entrain fragments and transport them up said central passage, the improvement comprising a sleeveform bit connector having double walls spaced apart to define a chamber, said connector being adapted to be connected between said bit and the lower end of said drill pipe and to receive said fluid in said chamber and said bit has axially elongate holding elements guidably movable in said sleeve so that when said bit is in an extended limit position, ports are opened between said elements in communication with said chamber and with said central passage and with the annulus of said borehole, whereby fluid currents in said ports scour said annulus.

2. Apparatus as set forth in claim 1, wherein said sleeve walls are pinned by radially-disposed pin elements passing through said chamber, and said holding elements comprise hooks slidable adjacent said pins and engageable with said pins when said bit is in said extended limit position.

3. Apparatus as set forth 11 claim 2 wherein said hooks comprise sectoral cylindrical segments projecting axially from the upper face of said bit.

4. Apparatus as set forth in claim 3' wherein said bit has an upper face provided with inner and outer annular seats which are engageable with the lower ends of said sleeve walls to form gas seals when said drill pipe rests on said bit.

5. Apparatus as set forth in claim 4 wherein said bit is guided non-rotatably in said chamber and said holding elements slide tangent to respective pins and one additional pin is provided along a side of a holding element remote from the respective pin.

6. Apparatus as set forth in claim 5 wherein the lower margin of the outer sleeve wall of said connector is conically bevelled and the outer seat of said bit face is complementarily shaped, the seat flaring radially outwardly upwardly.

7. Apparatus as set forth in claim 4 wherein said holding elements project from the upper face of said bit intermediate said inner and outer annular seats, and said upper face further comprises an axially elevated ring separating said seats between adjacent holding elements.

References Cited UNITED STATES PATENTS 884,152 4/1908 Hardsolg 296 X 1,862,260 6/1932 Edmonds 175-100 2,584,978 2/1952 Bassinger 175296 X 3,045,768 7/1962 Huffman 175100 NILE C. BYERS, JR., Primary Examiner 

